The present invention relates generally to a PEMF stimulator for treating osteoporosis and other medical conditions by promoting an increased bone mineral content and density.
Therapeutically difficult problems of the musculoskeletal system include spinal fusion, un-united fractures (or non-union fractures), failed arthrodeses, osteonecrosis, and chronic refractory tendinitis, decubitus ulcers and ligament, tendon injuries, osteoporosis, and Charcot foot. Such problems, especially fractures, may result from losses in bone mineral density. Osteoporosis in particular is responsible for 1.5 million fractures in the U.S. annually, especially hip, vertebral and wrist fractures. One conventional approach for treating such fractures is pharmaceutical therapy. This approach is disadvantageous because such therapy is generally expensive, and lasts for a patient""s lifetime. Furthermore, such therapy may be associated with side effects which some patients may not tolerate.
Pulsed electromagnetic fields (PEMF) are low-energy, time-varying magnetic fields that are useful for treating such problems of the musculoskeletal system. For PEMF therapy, an electromagnetic transducer coil is typically placed in the vicinity of the fracture or fusion such that pulsing the electromagnetic transducer will produce an applied field that penetrates to the underlying bone.
One conventional approach is to use a flat oval-shaped transducer coil for PEMF fracture therapy. This approach is disadvantageous because the transducer coil may not cover the entire treatment area and the applied field has limited penetration. A second, coil design for spinal fusion incorporated both a primary coil and a secondary coil to provide broad field coverage inside a defined treatment volume. Accordingly, providing effective PEMF fracture therapy using a flat coil design with broad field coverage and good field penetration required a new coil and drive circuit design which permits the use of only a single, more compact and energy efficient coil. This design is described in detail in U.S. Pat. No. 5,743,844, entitled High Efficiency Pulsed Electromagnetic Field (PEMF) Stimulation Therapy Method and System.
In accordance with the teachings of the present invention, disadvantages and problems associated with the use of conventional flat or oval shaped coils or utilization of both a primary and secondary coil design have been substantially reduced or eliminated.
One aspect of the present invention includes a bone mineral density (BMD) stimulator for osteoporotic patients. The stimulator for this embodiment may sometimes be referred to as a PEMF stimulator or Osteoporosis stimulator. The stimulator generates a pulsed electromagnetic field (PEMF) which induces voltages and current to provide non-invasive treatment to increase bone mineral density (BMD). The pulsed electromagnetic field generated by the bone mineral density stimulator, provides a non-invasive treatment for osteoporosis. The signal is preferably of a similar frequency as that delivered by commercially available stimulators which have been clinically demonstrated to affect bone formation. The signal offers greater energy efficiency than many current commercial PEMF devices.
A flat coil design with broad field coverage and good field penetration permits the use of only a single coil, and results in a compact and more energy efficient coil to produce such a pulsed electromagnetic field, as is described in U.S. Pat. No. 5,743,844. Use of such a design can be advantageous in treating many areas at high risk for fractures due to osteoporosis. Such areas include, but are not limited to, the thoracic and lumbar spine, femoral head, neck, and the upper and lower extremities. At least two such coils may be disposed in a pad in at least one layer of elastomeric material. For some applications, the pad may include a polymeric material that may be deformed to assume various configurations and/or to provide support. For additional applications, an additional coil may be disposed in an extremity pad.
Technical advantages of the present invention include using PEMF therapy to increase bone density to a level that substantially decreases a patient""s risk of fracture. For example, treatment over a broad field that would encompass all areas of bone particularly prone to osteoporotic fracture, including but not limited to areas such as the hip, spine and wrists, would be beneficial in increasing bone mineral density and/or content, thereby preventing osteoporotic fracture. Another technical advantage includes a synergistic effect when PEMF therapy is used in combination with pharmaceutical therapy. Yet another technical advantage includes using PEMF therapy to provide a patient a single daily treatment to simultaneously treat areas subject to fracture. The cost of such PEMF therapy is substantially reduced as compared to the cost associated with pharmaceutical treatment of osteoporosis. Such PEMF therapy may provide a suitable replacement therapy for patients who cannot be treated with pharmaceuticals. A bone mineral density stimulator incorporating teachings of the present invention may be used for prevention of hip, spinal, wrist and/or other fractures.
Further technical advantages of the present invention include producing an energy efficient PEMF signal with a pulse period between ten microseconds (10 xcexcsec) and twenty microseconds (20 xcexcsec). For some applications, a bone mineral density stimulator producing a PEMF signal with a pulse period of approximately sixteen microseconds (16 xcexcsec) will be very energy efficient.